Vehicle-based automatic traffic conflict and collision avoidance

ABSTRACT

Systems and methods for providing vehicle-centric collision avoidance are disclosed. An example method includes determining a first flight trajectory for a first aircraft, determining a second flight trajectory for a second aircraft, predicting a distance between the first aircraft and the second aircraft at a predicted closest point of approach based on the first and second flight trajectories, comparing the distance to a separation perimeter layer, the separation perimeter layer configured to provide a minimum separation distance from the first aircraft to the second aircraft, and altering the first flight trajectory when the distance breaches the separation perimeter layer.

RELATED APPLICATIONS

This patent arises from a continuation of U.S. patent application Ser.No. 13/739,741, filed Jan. 11, 2013, which is a divisional of U.S.patent application Ser. No. 11/864,335 (now U.S. Pat. No. 8,380,424),filed Sep. 28, 2007. The entireties of U.S. patent application Ser. No.13/739,741 and U.S. patent application Ser. No. 11/864,335 areincorporated by reference herein.

TECHNICAL FIELD

This present disclosure is related to systems and methods for guidanceaircraft, and more specifically, to systems and methods for guidingaircraft to avoid collisions.

BACKGROUND

Currently, human air traffic controller and ground-based air trafficcontrol systems play a major role in collision avoidance betweenaircraft. Pilots generally rely on their situational awareness and theinstructions provided by the air traffic controllers to avoid airtraffic conflicts. However, the ability of pilots to avoid potentialcollisions may be affected by human errors on the part of pilots and airtraffic controllers. Often, human errors are caused by factors such asfatigue, stress, or lack of experience.

Some aircraft may be equipped with avionic devices such as the trafficalert and collision avoidance system (TCAS) to reduce the danger ofpotential collision between aircraft. Typically, TCAS interrogates thesecondary surveillance radar transponders of nearby aircraft and alertsa pilot of an aircraft when potential flight path conflicts with otheraircraft are detected. Effective collision avoidance is then dependenton the pilot of the aircraft exchanging escape maneuver intentions withthe pilots of the conflict aircraft, as well as dependent on the pilotsmaking the proper escape maneuvers. Additionally, in some instances, theescape maneuvers elected by the pilots may not be compatible with otherair traffic, thus creating further collision potential. This problem maybe exacerbated by heavy air traffic conditions. Therefore, novel systemsand methods that provide automated vehicle-centric collision avoidancewithout the need for human involvement, thereby reducing the possibilityof human error, would have utility.

SUMMARY

The present disclosure is directed to systems and methods for providingautomated vehicle-centric collision avoidance between aircraft withoutthe need for human involvement. The automated vehicle-centric collisionavoidance system may reduce or eliminate the possibility of human errorand improperly selected escape maneuvers. Additionally, the need for airtraffic controllers to direct aircraft separations may be diminished,thereby easing their workload. Accordingly, air traffic controller maybe able to manage larger numbers of aircraft than previously possible.The ability to automatically avoid air traffic collisions may alsofacilitate the deployment of unmanned aircraft for both commercial andmilitary operations.

In accordance with various embodiments, a method for automaticallyproviding air traffic collision avoidance includes determining a firstflight trajectory for a first aircraft. The method also includesdetermining a second flight trajectory for a second aircraft. A distancebetween the first aircraft and the second aircraft at a closest point ofapproach (CPA) is predicted. The predicted closest point of approach isthen compared to a separation perimeter layer. The separation perimeterlayer is configured to provide a minimum separation distance from thefirst aircraft to the second aircraft. When the predicted closest pointof approach breaches the separation perimeter, the first flighttrajectory is altered to provide collision avoidance. In someembodiments, at least a portion of the first trajectory may bereinstated at any time the predicted distance at the closest point ofapproach no longer breaches the separation perimeter.

In additional embodiments, the method also includes predicting a seconddistance between the second aircraft and the first aircraft at anotherclosest point of approach (CPA) based on the first and second flighttrajectories. Next, the second distance is compared to anotherseparation perimeter layer. The other separation perimeter layer isconfigured to provide another minimum separation distance from thesecond aircraft to the first aircraft. When the distance at thepredicted closest point of approach breaches the other separationperimeter, the second trajectory is altered to provide collisionavoidance.

A computer readable medium that includes computer-executableinstructions that perform collision avoidance is disclosed in otherembodiments. The acts include determining a first flight trajectory fora first aircraft. The method also includes determining a second flighttrajectory for a second aircraft. A distance between the first aircraftand the second aircraft at a closest point of approach (CPA) ispredicted. The predicted closest point of approach is then compared to aseparation perimeter layer. The separation perimeter layer is configuredto provide a minimum separation distance from the first aircraft to thesecond aircraft. When the predicted closest point of approach breachesthe separation perimeter, the first flight trajectory is altered toprovide collision avoidance. In some embodiments, at least a portion ofthe first trajectory may be reinstated at any time the predicteddistance at the closest point of approach no longer breaches theseparation perimeter.

In additional embodiments, an aircraft is disclosed. The aircraftincludes a structural assembly, and at least one system for guidingaircraft at least partially disposed within the structural assembly. Theguidance system includes a prediction component configured to predict adistance between the first aircraft and the second aircraft at a closestpoint of approach (CPA) based on the first and second flighttrajectories. The guidance system also includes a comparison componentconfigured to compare the distance to a separation perimeter layer. Theseparation perimeter layer is configured to provide a minimum separationdistance from the first aircraft to the second aircraft. The systemfurther includes an alteration component configured to alter the firstflight trajectory when the distance breaches the separation perimeterlayer.

While specific embodiments have been illustrated and described herein,as noted above, many changes can be made without departing from thespirit and scope of the disclosure. Accordingly, the scope of thedisclosure should not be limited by the disclosure of the specificembodiments set forth above. Instead, the embodiments should bedetermined entirely by reference to the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of systems and methods in accordance with the teachings ofthe present disclosure are described in detail below with reference tothe following drawings.

FIGS. 1 a and 1 b are aerial views depicting exemplary concepts forproviding vehicle-centric collision avoidance, in accordance withvarious embodiments;

FIG. 2 is a block diagram depicting an exemplary avionics system inwhich methods for providing vehicle-centric collision avoidance, asshown in FIGS. 1 a and 1 b, may be implemented in accordance with anembodiment;

FIG. 3 is a block diagram depicting a vehicle-centric collisionavoidance system that issues avoidance commands, in accordance with anembodiment;

FIG. 4 illustrates exemplary equations for computing a closest point ofapproach between a plurality of aircraft and the generation of avoidancecommands, in accordance with an embodiment;

FIGS. 5 a and 5 b are block diagrams depicting a vehicle-centriccollision avoidance system that modifies flight trajectories, inaccordance with an embodiment;

FIG. 6 is a block diagram depicting a dynamic trajectory generator thatprovides trajectory planning for a plurality of vehicles, in accordancewith an embodiment; and

FIG. 7 is a side elevational view of an aircraft equipped with anavionics system that provides vehicle-centric collision avoidance, inaccordance with an embodiment.

DETAILED DESCRIPTION

Embodiments of systems and methods in accordance with the presentdisclosure are directed to automatically providing vehicle-centriccollision avoidance between aircraft without the need for humaninvolvement. Many specific details of certain embodiments are set forthin the following description and in FIGS. 1-7 to provide a thoroughunderstanding of such embodiments. The present disclosure may haveadditional embodiments, or may be practiced without one or more of thedetails described below.

Generally, embodiments of systems and methods in accordance with thepresent disclosure provide an automated vehicle-centric collisionavoidance system. Aircraft equipped with this automated vehicle-centriccollision avoidance system may automatically perform escape maneuvers toavoid collisions with other aircraft. In this way, the automaticvehicle-centric collision avoidance system may advantageously reduce oreliminate the possibility of human error and the performance of escapemaneuvers that can themselves create further potential for collision.Additionally, the need for air traffic controllers to direct aircraftseparations for collision avoidance may be diminished, thereby easingtheir workload. Accordingly, the automatic vehicle-centric collisionavoidance system may advantageously enable air traffic controllers tomanage larger numbers of aircraft than previously possible. Moreover,the ability to automatically avoid air traffic collisions may alsofacilitate the deployment of unmanned aircraft for both commercial andmilitary operations.

FIG. 1 a depicts a first exemplary concept for providing collisionavoidance using a vehicle-centric collision avoidance system inaccordance with an embodiment. Specifically, FIG. 1 a shows an aircraft102 and an aircraft 104. The aircraft 102 may be equipped with avehicle-centric collision avoidance system. Aircraft 102 is traveling ona flight path 106, while aircraft 104 is traveling on a flight path 108.The vehicle-centric collision avoidance system of the aircraft 102 maybe configured to predict a closest point of approach (CPA) 110. The CPA110 indicates the smallest range that occurs between the aircraft 102and the aircraft 104 as they continue on their flight path 106 andflight path 108, respectively. According to various implementations, theavoidance system of aircraft 102 may also predict a time-to-go beforereaching the CPA 110, or the time duration before the aircraft 102reaches the CPA 110. Moreover, the prediction of the CPA 110 may furtherinclude the computation of the current range and a separation directionat the time of CPA.

A separation perimeter 116 may be predefined in the vehicle-centriccollision avoidance system of the aircraft 102. Accordingly, the vehiclecentric collision avoidance system of the aircraft 102 may produceavoidance commands when the predicted separation range of the CPA 110 iswithin, or “breaches” the predefined separation perimeter 116. Thegenerated avoidance commands may be configured to alter the flight pathof the aircraft 102. The generated avoidance commands may also alter thespeed of the aircraft.

As shown in FIG. 1 a, the vehicle-centric collision avoidance system ofaircraft 102 may generate one or more commands 112 that cause theaircraft 102 to reactively alter its flight path 106 to a transformedflight path 114. In this way, the vehicle-centric collision avoidancesystem in the aircraft 102 may automatically ensure that properseparation is maintained between aircraft 102 and 104 at all times. Theproper separation may be in the form of desired separation perimeter116. The desired separation perimeter 116 may change location, asillustrated by separation perimeter 116 a, when the flight path 106 ofthe aircraft 102 is altered to flight path 114. The vehicle-centriccollision avoidance system of the aircraft 102 may continuously monitorfor traffic aircraft while the aircraft is on altered flight path 114.In this way, the aircraft 102 may return to its path 106 when theautomatic vehicle-centric collision system of the aircraft 102determines that the potential breach of the separation perimeter 116 ano longer exists. It will be appreciated that in other embodiments, aplurality of separation perimeter layers may be predefined in thevehicle-centric collision avoidance system of the aircraft 102. Forexample, the separation perimeter 116 may include multiple separationperimeter layers. As further described below, the plurality ofseparation perimeter layers may be defined based on temporal, aircraftvelocity, aircraft motion rates, and distance parameters.

FIG. 1 b depicts a second exemplary concept for providing collisionavoidance using a vehicle-centric collision avoidance system inaccordance with an embodiment. This exemplary concept demonstrates theavoidance interaction of a plurality of aircraft, wherein each of theaircraft is equipped with a vehicle-centric collision avoidance system.Specifically, FIG. 1 b shows an aircraft 118 and an aircraft 120, eachof which is equipped with a vehicle-centric collision avoidance system.The aircraft 118 is traveling on a flight path 122, while the aircraft120 is traveling on a flight path 124. The avoidance system in theaircraft 118 may be configured to predict a closest point of approach(CPA) 126. Likewise, the avoidance system in aircraft 120 may beconfigured to predict a CPA 128. The CPA 126 and the CPA 128 indicatethe smallest range that occurs between the aircraft 118 and the aircraft120 as they continues on their flight path 122 and flight path 124,respectively.

According to various implementations, the vehicle-centric collisionavoidance system in each of the aircraft 118 and 120 may also predict atime-to-go before reaching the CPA 126 and CPA 128, respectively.Moreover, the predictions of the CPA 126 and CPA 128 may further includethe computation of the current range and a minimum separation directionat the time of CPA.

A separation perimeter 130 may be predefined in the vehicle-centriccollision avoidance system of the aircraft 118. Similarly, a separationperimeter 132 may be predefined in the vehicle collision avoidancesystem of the aircraft 120. Accordingly, the vehicle-centric collisionavoidance system in the aircraft 118 may produce avoidance commands whenthe predicted separation range of the CPA 126 is within, or “breaches” apredefined separation perimeter 130.

In a corresponding fashion, the vehicle-centric collision avoidancesystem in the aircraft 120 may produce avoidance commands when thepredicted separation range of the CPA 128 is within, or “breaches” apredefined separation perimeter 132. Each set of the generated avoidancecommands may be configured to alter the flight paths of the aircraft 118and 120, respectively. The generated avoidance commands may also alterthe speed of each aircraft.

For example, as shown in FIG. 1 b, the vehicle-centric collisionavoidance system of aircraft 118 may generate one or more commands 134that cause the aircraft 118 to reactively alter its flight path 122 to atransformed flight path 136. Likewise, the vehicle-centric collisionavoidance system of aircraft 120 may generate one or more commands 138that cause aircraft 120 to alter its flight path 124 to transformedflight path 140. In this way, the vehicle-centric collision avoidancesystem in each aircraft may automatically ensure that proper separationis maintained between aircraft 118 and 120 at all times. The properseparation may be in the form of desired separation perimeters 130 and132, respectively. However, each aircraft 118 and 120 may return totheir original paths 122 and 124, respectively, when the automaticvehicle-centric collision system in each aircraft determines that thepotential breaches of the corresponding separation perimeters 130 and132 no longer exist.

It will be appreciated that in other embodiments, a plurality ofseparation perimeter layers may be predefined in the vehicle-centriccollision avoidance system of each aircraft 118 and 120. For example,each of the separation perimeters 130 and 132 may include multipleseparation perimeter layers. As further described below, the pluralityof separation perimeter layers may be defined based on temporal,aircraft velocity, aircraft motion rates, and distance parameters.

Accordingly, the capability to automatically alter aircraft paths mayadvantageously reduce or eliminate the risk of collisions due to humanerror or miscommunication associated with current collision avoidancesystems. Additionally, the vehicle-centric avoidance system may decreasethe workload of ground controllers by diminish their involvementmitigating potential aircraft collision.

FIG. 2 is a block diagram depicting an exemplary avionics system inwhich methods for providing vehicle-centric collision avoidance, asshown in FIGS. 1 a and 1 b, may be implemented. The avionics system 200includes a navigation system 202 that include a flight path database204, an autopilot 206, a flight director 208, traffic sensors 210, andan exemplary collision avoidance computer 212. According to variousembodiments, methods for providing altered flight paths in accordancewith the teachings of the present disclosure may be implemented in theexemplary collision avoidance computer 212.

The navigation system 202 may be used to provide the geographicalposition of the aircraft during flight. The navigation system 202 mayinclude an Inertial Reference System (IRS), an Attitude Heading andReference System (AHRS), a Global Positioning System (GPS), and othersimilar systems. In various embodiments, the navigation system 202 mayinclude an onboard flight path database 204 that provides predeterminedcourses for the aircraft.

The autopilot 206 is generally configured to pilot the aircraft withouthuman intervention. In various implementations, the autopilot 206 mayobtain flight information (e.g., position, heading, attitude, and speed)from the navigation system 202. The autopilot 206 may also obtain courseinformation from the flight path database 204. By comparing the flightinformation with the course information, the autopilot 206 may computeflight trajectories and issue control commands (e.g., throttle settingsand flight control surface commands) to an aircraft's flight controlsystem to maintain the aircraft on a particular flight path.

The flight director 208 is generally configured to compute and displaythe proper path for the aircraft to one or more pilots during a specificflight. For example, when a pilot is holding a course, the flightdirector 208 may interact with the flight path database 204 and theautopilot 206 to computer and display the necessary flight maneuvers tothe pilot. The flight director 208 may include a flight directorindicator (FDI), a horizontal situation indicator (HSI), a modeselector, and a flight director computer. Moreover, the FDI may includea display that may present an attitude indicator, a fixed aircraftsymbol, pitch and bank command bars, a glide slope indicator, alocalizer deviation indicator, and the like. The flight director 208 mayfurnish a pilot with steering commands necessary to obtain and hold adesired path. In some embodiments, the flight director 208 may furtherprovide steering commands to the autopilot 206, which the autopilot 206may translate into flight control system commands.

The traffic sensors 210 may be configured to obtain positions of trafficaircraft. According to various embodiments, the traffic sensor 210 maybe configured to receive traffic data from a Traffic Alert and CollisionAvoidance System (TCAS), an Automatic Dependent Surveillance (ADS)system, a ground air traffic control (ATC) system, or an on-boardtraffic surveillance radar system, as well as other air trafficdetection systems.

As further shown in FIG. 2, the collision avoidance computer 212 hasprocessing capabilities and memory suitable to store and executecomputer-executable instructions. In one embodiment, the collisionavoidance computer 212 includes one or more processors 214 and memory216. The memory 216 may include volatile and nonvolatile memory,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer-readableinstructions, data structures, program modules or other data. Suchmemory includes, but is not limited to, random access memory (RAM),read-only memory (ROM), electrically erasable programmable read-onlymemory (EEPROM), flash memory or other memory technology, compact disc,read-only memory (CD-ROM), digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, redundant array ofindependent disks (RAID) storage systems, or any other medium which canbe used to store the desired information and which can be accessed by acomputer system.

The memory 216 contains modules that enable the collision avoidancecomputer 212 to perform various functions. These modules may include anautopilot interface module 218, a database interface module 220, aflight director interface module 222, a collision avoidance module 224,a command integration module 226, a traffic sensor interface module 228,and a database 230. These modules may be implemented as software orcomputer-executable instructions that are executed by the one or moreprocessors 214 to perform the functions as described below.

The autopilot interface module 218 is configured to enable the collisionavoidance computer 212 to communicate with the autopilot 206. Thecommunication may be established over an electrical connection, anoptical connection, and the like. According to various embodiments, theautopilot interface module 218 may be configured to enable the autopilot206 to perform collision avoidance under the direction of the collisionavoidance computer 212.

The database interface module 220 enables the reading of data from andwriting of data to the database 230. According to various embodiments,the database interface module 220 may be activated by the other modulesin memory 216, as further described below. The database 230 may beconfigured to store information that may be used to maintain an aircrafton various flight paths as well as to avoid collisions. For instance,the database 230 may contain trajectory and speed laws. The trajectoryand speed laws may dictate the performance and maneuver capabilities ofan aircraft. Moreover, the database 230 may also store aircraftseparation limits and aircraft response limits. The aircraft separationlimits are configured to define a separation perimeter, such as theseparation perimeter 116 described in FIG. 1 a. These stored parametersmay dictate the dimensions and shape of the separation perimeter. Forexample, the parameters may specify measurements such as diameter,width, length, and height, and the like. The aircraft response limits,as further described below, may dictate the proximity and time at whichan aircraft alters its flight path to militate collision potential.

The flight director interface module 222 may facilitate thecommunication between the flight director 208 and the collisionavoidance module 224. Accordingly, the flight director interface module222 may enable the flight director 208 to provide a pilot with thenecessary steering commands.

The collision avoidance module 224 may be employed to analyze thetraffic sensor data received from the traffic sensor module 222.Accordingly to various implementations, the collision avoidance module224 may alter the flight path of an aircraft if the aircraft cannotmaintain a desired separation perimeter 116, as described in FIG. 1 a.Specifically, the functions of the collision avoidance module 224 aredescribed below in FIG. 3.

The command integration module 226 may be configured to use theautopilot interface module 218 and the flight director interface module222 to respectively integrate collision avoidance commands, flighttrajectory changes, or new flight trajectories, to the autopilot 206 andthe flight director 208. The traffic sensor interface module 228 may beconfigured to provide traffic data from the traffic sensors 210 to thecollision avoidance computer 212. In turn, the traffic sensor interfacemodule 228 may be used to provide the data from the traffic sensors 210to the collision avoidance module 224.

FIG. 3 is a block diagram depicting a vehicle-centric collisionavoidance system 300 that provides avoidance commands. The system 300may include a flight control component 302. The flight control component302 is generally configured to maintain an aircraft on predeterminedflight paths as the aircraft travels between various destinations.Additionally, the system 300 may also include a collision avoidancecomponent 304. In some embodiments, the collision avoidance component304 may be carried out by the collision avoidance module 224 illustratedin FIG. 2. As further described below, the collision avoidance component304 may interact with the flight control component 302 to alter thetrajectory of the aircraft to provide collision avoidance.

The flight control component 302 may include a trajectory generatorfunction 306, a control command function 308, and a command modificationfunction 310. According to various implementations, the functions306-310 may be carried out by one or more of a navigation system 202,the autopilot 206, and the flight director 208, as described above inFIG. 2.

The trajectory generator function 306 is configured to produce predictedflight paths for the aircraft. The flight paths produced may be referredto as “4D trajectories”, as the flight paths may dictate the position ofthe aircraft at a particular time.

The control command function 308 is configured to compare a generatedflight path with the current position and velocity of the aircraft todetermine the deviation and the needed flight path corrections. Thecontrol command function 308 may produce control commands that implementthe flight path corrections according to trajectory and speed controllaws. According to various implementations, the control commands may beconfigured to change throttle settings, as well as manipulate the flightcontrol surfaces of an aircraft.

In some implementations, the control commands produced by the controlcommand function 308 may be further processed by the assignment function310 before they are implemented on the respective flight controlsurfaces and propulsion system. Specifically, the assignment function310 may be configured to implement the control commands as a function offlight conditions using gains (weights) and limits. For example, theassignment function 310 may assign a high weight value to one or morecontrol commands when the aircraft has severely deviated from a flightpath. The high weight value may cause the one or more control commandsto be expediently implemented to a high degree so as to cause theaircraft to quickly return to the designated flight path. Conversely,the assignment function 310 may assign a low weight value to one or morecontrol commands when the aircraft experiences only a slight deviationfrom the flight path. In such an instance, the control commands may begradually implemented so that the return of the aircraft to thedesignated flight path is more measured.

As further shown in FIG. 3, the collision avoidance component 304 of thesystem 300 may issue avoidance commands that compete with the controlcommands provided by the flight control component 302. In this way, theavoidance commands may alter a flight trajectory to provide collisionavoidance. As described below, the issue of avoidance commands may becarried out by functions 312-322 of the collision avoidance component304.

The trajectory analysis function 312 may be configured to predict theflight path of the aircraft with respect to the flight paths of othertraffic aircraft. The trajectory analysis function 312 may obtaintraffic knowledge 314 from the traffic sensor 210 via the traffic sensorinterface module 228. Traffic knowledge may include the position,velocity, heading, heading rates of change, climb rates, descend rates,velocity rate of change, and trajectory of the traffic aircraft. Inother instances, traffic knowledge may also include the flight plans ofparticular traffic aircraft. For example, if a traffic aircraft hasfiled a flight plan, the trajectory analysis function 312 may obtain theflight plan from a ground source (e.g., a flight plan database). Theflight plan may provide trajectory analysis function 312 with detailknowledge regarding the positions of the traffic aircraft at particularmoments in time. However, in additional examples where the FMS (flightmanagement function) of each traffic aircraft is capable of transmittingposition and rate data to other aircraft, the trajectory analysisfunction 312 may also obtain the flight knowledge directly from eachtraffic aircraft.

Additionally, the trajectory analysis function 312 may acquire thepredicted trajectory of the aircraft that includes the function 312,i.e., self-aircraft trajectory, from the trajectory generator function306. Once the trajectory analysis function 312 has received trajectorydata from the various sources, the function 312 may process the data todetermine the desired trajectory information. This trajectoryinformation may include (1) the position of the self-aircraft; (2) therates of self-aircraft, (3) the planned trajectory of the self-aircraft;(3) the position of each traffic aircraft, (4) the rates of each trafficaircraft; and (5) the planned trajectory of each traffic aircraft. Inother words, the trajectory analysis module 312 may predict the expectedflight path of each aircraft for which it has provided with data.Moreover, the trajectory analysis function 312 may be configured to passthe predicted trajectories to a computations function 316. As usedherein, rates for the self-aircraft and each traffic aircraft mayinclude rates of heading change, climb rates, descend rates, velocity,and rates of velocity change (i.e., acceleration).

The computations function 316 may be configured to process the predictedtrajectories of the aircraft and provide aircraft avoidance commands.Specifically, the predicted trajectories of the aircraft may be employedto predict whether at their closest point of approach (CPA), a pluralityof aircraft are expected to “breach” a predetermined separationperimeter, such as the separation perimeter 116 described in FIG. 1 a.For instance, if the aircraft are predicted to be simultaneously insidethe separation perimeter at their CPA, then the separation perimeter isexpected to be “breached.” When the computations function 316 reachessuch a prediction, the function may be configured to issue avoidancecommands. The avoidance commands may preemptively alter the flight pathsof the aircraft so that no separation perimeter is “breached” at thefuture CPA of the aircraft.

Specifically, as described above, the flight paths alteration of anaircraft, as provided by the computations function 316, is illustratedin FIG. 1 a. As shown in FIG. 1 a, aircraft 102 and aircraft 104 areexpected to “breach” the desired separation perimeter 116, (as they willbe simultaneously inside the perimeter) at their CPA. Accordingly, thecomputations function of a collision avoidance system in aircraft 102,such as the computations function 316, may alter the aircraft 102 fromflight path 106 to flight path 114. An exemplary CPA calculation, aswell as an exemplary generation of avoidance commands, as performed bythe computations function 316, is described in FIG. 4.

FIG. 4 illustrates exemplary equations for computing a closest point ofapproach between an aircraft 402 and an aircraft 404. Moreover, FIG. 4also illustrates the generation of avoidance commands. As shown in FIG.4, the closest point of approach vector (d_(m)) between aircraft 402 and404 may be represented by the equation (assuming aircrafts continuealong a straight paths with constant velocities):

$\begin{matrix}{{\overset{\_}{d}}_{m} = {{\overset{\_}{R} + {\overset{\_}{d}}_{c}} = {\overset{\_}{R} - {\frac{\overset{\_}{R} \cdot {\overset{\_}{V}}_{2r}}{{\overset{\_}{V}}_{2r} \cdot {\overset{\_}{V}}_{2r}}{\overset{\_}{V}}_{2r}}}}} & (1)\end{matrix}$wherein V _(2r) is the velocity vector of the aircraft 404 relative tothe aircraft 402, and R is the range vector between aircraft 402 and404. Furthermore, the time at the closest point of approach (t_(cpa))may be represented by the equation:

$\begin{matrix}{{t_{cpa} = {{- \frac{{\overset{\_}{d}c}}{{\overset{\_}{V}}_{2r}}} = {- \frac{\overset{\_}{R} \cdot {\overset{\_}{V}}_{2r}}{{\overset{\_}{V}}_{2r} \cdot {\overset{\_}{V}}_{2r}}}}}{wherein}\frac{{\overset{\_}{d}c}}{{\overset{\_}{V}}_{2r}}} & (2)\end{matrix}$is the norm of the distance dc between the aircraft 402 and the aircraft404 over the norm of the velocity, V _(2r) of the aircraft 404 relativeto the aircraft 402.

The control avoidance control law for the generation of avehicle-centric avoidance command, F _(control), may be represented bythe equation:

$\begin{matrix}{{{\overset{\_}{F}}_{control} = {- {\sum\limits_{1}^{n}\;{\sum\limits_{1}^{p}\;{K_{p,n} \cdot {\overset{\_}{C}}_{p,n}}}}}}{where}} & (3) \\{{\overset{\_}{C}}_{p,n} = {{{Cx}_{p,n} \cdot {\overset{\_}{i}}_{x}} + {{Cy}_{p,n} \cdot {\overset{\_}{i}}_{y}} + {{Cz}_{p,n} \cdot {\overset{\_}{i}}_{z}}}} & (4)\end{matrix}$and wherein p represents the number of perimeter layers, and nrepresents the number of traffic aircraft used in the generation of anavoidance command. Additionally, K_(p,n) contain the control gainsapplied to each respective control direction (ī_(x), ī_(y), ī_(z)) foreach respective traffic aircraft n under evaluation by the self-aircraftand for any of a number of respective perimeter layers p. Additionally,C _(p,n) contain the corresponding collision avoidance commandcomponents used in the generation of one or more avoidance commands.

According to various embodiments, C _(p,n) may be selected as follows:

$\begin{matrix}{{\overset{\_}{C}}_{p,n} = {\left( {d_{p} - {{\overset{\_}{d}m_{n}}}} \right)\frac{\overset{\_}{d}m_{n}}{{\overset{\_}{d}m_{n}}}}} & (5)\end{matrix}$where d_(p) is the desired separation distance for each perimeterevaluated, and which may be measured along the closest point of approach(CPA) distance vector dm_(n). If the control gains are equal in eachdirection and the same for each traffic aircraft then a single avoidancegain may be defined as follows:K _(p,n) =k _(avoidance), for all (p,n)  (6)

Thus, in this example, the avoidance command may reduce to:

$\begin{matrix}{{\overset{\_}{F}}_{control} = {{- k_{avoidance}}{\sum\limits_{1}^{n}\;{\sum\limits_{1}^{p}\;{\left( {d_{p} - {{\overset{\_}{d}m_{n}}}} \right)\frac{\overset{\_}{d}m_{n}}{{\overset{\_}{d}m_{n}}}}}}}} & (7)\end{matrix}$Further by example, if there is only one traffic aircraft underevaluation, that is, n=1, and only one separation perimeter isevaluated, p=1, (as illustrated in FIG. 1 a), then the avoidance commandmay reduce to:

$\begin{matrix}{{\overset{\_}{F}}_{control} = {{- {k_{avoidance}\left( {d_{1} - {{\overset{\_}{d}m_{1}}}} \right)}}\frac{\overset{\_}{d}m_{1}}{{\overset{\_}{d}m_{1}}}}} & (8)\end{matrix}$wherein k_(avoidance) contains the gain or control weight, d₁ is thedesired separation distance that may constitute the separationperimeter, and ∥ dm₁∥ is the norm of the closest point of approachdistance dm.

As shown, F _(control) provides the force or avoidance command, alongthe direction of dm to increase the dm between the aircraft 402 and 404.Moreover, according to the above equation, as the closest point ofapproach distance ∥ dm∥ becomes increasingly smaller, the magnitude ofthe avoidance command, F _(control), will proportionally increase. Inother words, according to various embodiments, the computations function316 may increase the magnitude of the avoidance command as CPA distancedecreases. For example, the computations function 316 may provide anavoidance command in the form of an acceleration command that increasesthe thrust of the aircraft 102. According to various embodiments, theavoidance command functions ( C _(p,n)) may be exponential functions,quadratic functions, or other functions that adjust the command as theself-aircraft approaches the CPA. In other embodiments, the avoidancecommand functions may be functions of other parameters and vectors suchas relative velocity and range.

According to some embodiments, the exemplary equations illustrated abovemay be implemented to establish multiple separation perimeter layers.Each perimeter layer may be maintained based on a unique set of values,gains, functions, and separation limits. Moreover, perimeter layers maybe established based on time, distance, rate, and any combinationthereof. For example, a temporal perimeter layer may be established whenthe time to closest point of approach is less than a specifiedseparation limit. A rate and distance perimeter layer may beestablished, for example, when avoidance command initiation is based onboth the magnitude of the relative rate and the range between theself-aircraft and any traffic aircraft. In addition, the desiredseparation distance of a spatial separation perimeter may include a setof distances and reference directions (ī_(x), ī_(y), ī_(z)) thatestablish the separation perimeter shape, wherein each direction mayhave its own avoidance gain. In this way, it will be appreciated that aplurality of different separation perimeter layers may be respectivelyestablished between the self-aircraft and each traffic aircraft.

Returning to FIG. 3, the separation perimeter, such as the desiredseparation perimeter 116 illustrated in FIG. 1 a, may be establishedbased on separation limits 318. To put it another way, the separationlimits 318 may define the dimensions of the separation perimeter 116. Inone implementation, the separation limits 318 may define a minimumseparation distance that extends in all directions. In such animplementation, the separation perimeter may be in the form of a sphere.For example, a separation perimeter may be established with all trafficaircraft based on the separation distance of one mile in all directions.In other words, a plurality of aircraft are considered to have“breached” a separation perimeter if they are closer than one mile attheir CPA.

In other implementations, the separation limits 318 may be configured toprovide other separation perimeter shapes. For example, the separationlimits 318 may define a radius that extends in all longitudinal andlatitudinal directions, and a fixed distance in the vertical axis forall points that extend from the longitudinal and latitudinal directions.In such an instance, the separation limits 318 may define a cylindricalspace. However, it will be appreciated that the separation limits 318may be configure to define a variety of other three-dimensional shapes(e.g., ellipsoid, spheroid, half sphere, cubes, octahedron, etc.) Thethree-dimensional shapes may not be symmetrical. Specifically, thethree-dimensional shapes of the separation limits 318 may be definedbased on self-aircraft and traffic aircraft class, (e.g., heavycommercial aircraft, light private aircraft, etc.), maneuverability ofthe self-aircraft and traffic aircraft, as well as the speed of theself-aircraft and traffic aircraft.

The computations function 316 may be further configured to utilizeresponse limits 320 in the calculation of avoidance commands. Responselimits 320 may determine the promptness at which the avoidance commandsare carried out. For example, the response limits 320 may be establishedso that when the predicted CPA between the self-aircraft and a trafficaircraft is likely to occur at a large range (distance) away from theself-aircraft's current position, the computations function 316 maydelay the provision of the one or more avoidance commands. Conversely,if the predicted CPA between the self-aircraft and the traffic vehicleis likely to occur at a small distance from the self-aircraft's currentposition, the computations function 316 may immediately provide the oneor more avoidance commands to for execution.

In some embodiments, the computations function 316 may be configured tocompute the time-to-go, that is, the time duration before the aircraftreaches the CPA. This time duration may be referred to astime-to-closest point of approach (TCPA). In such embodiments, theresponse limits 320 may also include time limitations. For example, ifthe CPA is likely to occur far in the future, such as beyond apredetermined time interval, the computations function 316 may delayavoidance command execution. Conversely, if the CPA is imminent in time,such as before a predetermined time interval expires, the computationsfunction 316 may more rapidly provide the avoidance commands forexecution. Furthermore if the TCPA is negative then the CPA has alreadyoccurred and the aircraft are thence moving away from one another. Inthis case, the avoidance command may be set to zero. The fixed timeinterval may be any time increment (e.g., seconds, minutes, etc.). Inthis way, the computations module 316 may prioritize avoidance based onthe imminence of the potential collision with each of a plurality oftraffic aircraft. For example, the computation of TCPA and theimplementation of time limitations as response limits 320 may besuitable for collision avoidance between aircraft with long TCPAduration such as those that are flying in formation at close range alongparallel paths, and in trail, or head on trajectories at far range withnear zero closest point of approach distance.

The avoidance modification function 322 may be configured to assigngain, or avoidance weights, to the one or more avoidance commandsgenerated by the computations function 316. The avoidance weights arerepresented by K_(p,n) described in FIG. 3. Avoidance weights may beused to establish the relative strength of the avoidance and steeringcommands. For example, the avoidance modification function 322 maycontain a low gain for a long range first perimeter layer and a highgain for a near range second perimeter layer. In this example, the firstperimeter layer may enable separation using minor path corrections atfar range. Also in this example, the second perimeter layer may insurethe ability of the avoidance commands to overcome the normal controlcommands issued by the control command function 308 at near range usinghigher gains.

In this way, the avoidance computations function 316 and avoidancemodification function 322 may increase the tendency of the self-aircraftto alter its flight path as it closes in on the traffic aircraft.Moreover, it will be appreciated that the avoidance modificationfunction 322 may be configured to assign various gains to the avoidancecommands for each perimeter and each traffic aircraft.

In other embodiments, the avoidance modification function 322 may befurther configured to assign gains that selectively implement a portionof the avoidance commands. For example, the avoidance modificationfunction 322 may be configured to assign no weight to an avoidancecommand component that causes an aircraft to dive when the aircraft isbelow a predetermined minimum altitude. This may prevent the aircraftfrom performing unsafe flight path alterations. In alternativeimplementations, the weight assignment function 322 may be configured toassign zero weight to avoidance command components that turn theaircraft in a particular direction (e.g., right, left).

The avoidance modification function 322 may be further configured toconstrain the avoidance commands with control limits. For example, theavoidance modification function 322 may provide control limits thatprevent avoidance commands from being implemented when the deviationsfrom the flight path are negligible. In other examples, the command andavoidance modification functions 322 and 310 may use control limits toprevent radical movements of the aircraft or command saturation of theflight control system in the aircraft.

Once the avoidance modification function 322 has assigned the necessarygain and/or limits to the avoidance commands, the avoidance commands arepassed from the collision avoidance module 224 to the commandintegration module 226 shown in FIG. 2. The command integration module226 may be configured to implement a command integration process 324.Specifically, the command integration module 226 is configured to applythe avoidance commands to the control commands. As described above, thecontrol commands are produced by the control command function 308 andmodified by the command modification function 310. The avoidancecommands may include heading rate change commands, climb or descend ratemodification commands, acceleration and deceleration commands, and othersteering commands such as speed, altitude, and heading alterationcommands. In other words, the avoidance commands may be configured toaffect computations of thrust and flight control surface settings incommand integration process 324.

In various embodiments, the command integration module 226 may implementthe avoidance commands so that they compete with the control commandsissued by the control command function 308 as weighted and limited bycommand modification function 310. In this way, the collision avoidancemodule 224 may alter the flight path of an aircraft when the collisionavoidance 224 predicts that a “breach” of the desired separationperimeter 116, as described in FIG. 1 a, is expected.

Additionally, the command integration module 226 may also provideposition and rate readings back to the control command function and thetrajectory analysis function 312. In some implementations, since thecontrol command function 308 may be carried out by an aircraft flightcontroller (e.g., one or more of an autopilot 206, flight director 208,etc.), the position and velocity readings may be passed back to thosesystems. In turn, the control command function 308 may use the readingsto generate further control commands in the same process as describedabove. Likewise, the trajectory analysis function 312 may use thefeedback position and velocity readings to continuously update itsflight trajectory predictions.

It will be appreciated that collision avoidance module 224 may beconfigured to continuously monitor the trajectories of the self-aircraftand the traffic aircraft and predict future “breaches” of the separationperimeter by the CPA between the aircraft. This continuous monitoringmay ensure that the flight path of the aircraft is altered each time aCPA breach of the separation perimeter occurs. However, the collisionavoidance module 224 may terminate the output of the avoidance commandswhen the trajectories of the aircraft and the traffic aircraft indicatesthat the separation perimeter is no longer being breach by the CPA. Inthis, small flight path alterations may be continuously made to militateagainst potential collisions. In some embodiments, the collisionavoidance module 224 may implement the avoidance commands even when apilot is in control of the aircraft.

FIGS. 5 a and 5 b are block diagrams depicting a vehicle-centriccollision avoidance system that modifies flight trajectories. As shown,the vehicle-centric collision avoidance system 500 may include a flightcontrol system. The flight control system may be configured to maintainan aircraft on predetermined flight trajectories as the aircraft travelsbetween various destinations. Specifically, the flight control systemsmay include a trajectory generator function 502 and a vehicle responsefunction 504. The system 500 may also include a collision avoidancecomponent 506. The collision avoidance component 506 may be configuredto modify the flight trajectories, as provided by the flight controlcomponent 502 to provide collision avoidance. According to variousimplementations, the functions 502-504 may be carried out by one or moreof a navigation system 202, the autopilot 206, and the flight director208, as described above in FIG. 2.

The trajectory generator function 502 is configured to produce predictedflight paths for an aircraft. The flight paths produced may be referredto as “4D trajectories”, as the flight paths may dictate the position ofthe aircraft at a particular time. The vehicle response function 504 maybe configured to compare a generated flight path with the currentposition and velocity of the aircraft to determine any deviation and theneeded flight path correction. Based on this, the vehicle responsefunction 504 may produce control commands that implement the flighttrajectories according to trajectory, speed control laws, other controllaws, as well as vehicle dynamics. According to various implementations,the control commands may be configured to change the throttle settings,as well as manipulate the flight control surfaces of the aircraft.

The collision avoidance component 506 may modify the generated flightpath for the aircraft, as produced by trajectory generator function 502,before they are implemented as control commands by the vehicle responsefunction 504 to fly a trajectory 526. In such implementations, thecollision avoidance component 506 may be carried out by the collisionavoidance module 224 described in FIG. 2. FIG. 5 b illustrates thevarious functions 508-514 that may be carried out by the collisionavoidance component 506.

The trajectory analysis function 508 may be configured to predict theflight path of the aircraft with respect to the flight paths of othertraffic aircraft. The trajectory analysis function 508 may obtaintraffic knowledge 516 from the traffic sensor 210 via the traffic sensorinterface module 228. Traffic knowledge may include the position,velocity, heading, and trajectory of the traffic aircraft. In otherinstances, traffic knowledge may also include the flight plans or intentof particular traffic aircraft. For example, if a traffic aircraft hasfiled a flight plan or an updated intention, the trajectory analysisfunction 508 may obtain the flight plan from a central source (e.g., aflight plan database) or from the FMS on the traffic aircraft via a datalink. The flight plan may provide trajectory analysis function 508 withdetail knowledge regarding the positions of the traffic aircraft atparticular moments in time.

Additionally, the trajectory analysis function 508 may acquire thepredicted trajectory of the aircraft, i.e., self-aircraft trajectory,from the trajectory generator function 502. Moreover, the trajectoryanalysis function 508 may also acquire position and velocity data 518for the aircraft from one of the autopilot 206 and flight director 208.Once the trajectory analysis function 508 has received trajectory,position, and velocity data from the various sources, the function mayprocess the data and determine the desired trajectory information. Thistrajectory information may include (1) the position and rates of theself-aircraft; (2) the planned trajectory of the self-aircraft; (3) theposition and rates of each traffic aircraft; and (4) the plannedtrajectory of each traffic aircraft. In other words, the trajectoryanalysis module 512 may predict the expected flight path of eachaircraft for which it has provided with data. Moreover, the trajectoryanalysis function 508 may be configured to pass the predictedtrajectories to a computations function 510.

The computations function 510 may be configured to process the predictedtrajectories of the aircraft and provide aircraft avoidance commands.Specifically, the predicted trajectories of the aircraft may be employedto predict whether at their closest point of approach (CPA), theaircraft and at least one second traffic aircraft are expected to“breach” a predetermined separation perimeter, such as the separationperimeter 116 described in FIG. 1 a. For instance, if the secondaircraft is predicted to be inside the separation perimeter at theirCPA, then the separation perimeter is expected to be “breached”. Whenthe computations function 510 reaches such a prediction, the functionmay be configured to issue avoidance commands. The avoidance commandsmay preemptively alter the flight paths of the aircraft so that noseparation perimeter is “breached” at the future CPA of the aircraft.

Specifically, as described above, the flight paths alteration of anaircraft, as provided by the computations function 510, is illustratedin FIG. 1 a. As shown in FIG. 1 a, aircraft 104 is expected to “breach”the desired separation perimeter 116 at their CPA. Accordingly, the CPAcomputation function of a collision avoidance system in aircraft 102,such as the computations function 510, may alter the aircraft 102 fromflight path 106 to flight path 114. Similarly, as shown in FIG. 1 b, ifa collision avoidance system that includes a computations function, suchas the computations function 510, resides in each of the aircrafts 118and 120, each respective aircraft function may alter their own path in acomplementary fashion, i.e., each alters its path to one that does notcause further collision conflict with the altered path of anotheraircraft. An exemplary CPA calculation, as well as an exemplarygeneration of avoidance commands, as performed by the computationsfunction 510, are described in FIG. 4.

The separation perimeter, such as the desired separation perimeter 116illustrated in FIG. 1 a, may be established based on separation limits520. In other words, the separation limits 520 may define the dimensionsof the separation perimeter. In one implementation, the separationlimits 520 may define a minimum separation distance that extends in alldirections. In such an implementation, the separation perimeter may bein the form a sphere. For example, a separation perimeter may beestablished based on the separation distance of one mile in alldirections. In such as case, a plurality of aircraft are considered tohave “breached” a separation perimeter if they are closer than one mileat their CPA. In additional implementations, the separation perimetermay be configured with a plurality of layers based on temporal, aircraftvelocity, aircraft motion rates, and distance parameters, as describedabove in FIG. 4.

The computations function 510 may be further configured to utilizeresponse limits 522 in the calculation of avoidance commands. Responselimits 522 may determine the promptness at which the avoidance commandsare carried out. For example, the responses limits 516 may beestablished so that when the predicted CPA between the self-aircraft anda traffic aircraft is likely to occur at a large range, that is,distance away from the self-aircraft's current position, thecomputations function 510 may delay the provision of the one or moreavoidance commands for execution. Conversely, if the predicted CPAbetween the self-aircraft and the traffic vehicle is likely to occur ata small distance from the self-aircraft's current position, thecomputations function 510 may immediately provide the one or moreavoidance commands for execution. In other embodiments, response limits522 may also include time limitations. For example, if the CPA is likelyto occur far in the future, such as beyond a predetermined timeinterval, the computations function 510 may delay avoidance commandexecution. Conversely, if the CPA is imminent in time, such as before apredetermined time interval expires, the computations function 510 maymore rapidly provide the avoidance commands for execution. The fixedtime interval may be any time increment (e.g., seconds, minutes, etc.).

In this way, the computations function 510 may initiate avoidance basedon the imminence of the potential collision with each of a plurality oftraffic aircraft. For example, the implementation of time limitations asresponse limits by the computations function 510 may be suitable forcollision avoidance between aircraft with long TCPA such as those thatare flying in formation at close range along parallel paths, or head ontrajectories at far range with near zero closest point of approachdistance.

The avoidance modification function 512 may be configured to assigngain, or avoidance weights, to the one or more avoidance commandsgenerated by the computations function 510. The avoidance weights(K_(p,n)) may be represented by K_(avoidance) as shown in FIG. 3.Avoidance weights may be used to determine the strength of the avoidancecommand. According to various embodiments, the avoidance modificationfunction 512 may increase the gain in one or more avoidance commands asthe CPA (time or distance) between the self-aircraft and a trafficaircraft decreases. For example, a first set of avoidance computations,limits, and gains may enable separation using minor path correctionsupon a breach of a separation perimeter layer that is far in range. Inanother example, a second set of avoidance computations, limits, andgains may provide high-gain avoidance commands to overcome the normalcontrol commands issued by the control command function 308 upon thebreach of a near range separation perimeter.

In this way, the avoidance computations function 510 and avoidancemodification function 512 may increase the tendency of the self-aircraftto alter its flight path as it closes in on the traffic aircraft.Moreover, it will be appreciated that the avoidance modificationfunction 512 may be configured to assign different gains to othergenerated avoidance commands based on the specific separation perimeterlayer being breached.

The trajectory modification function 514 includes adjustment algorithmsthat are configured to modify the flight trajectories generated by thetrajectory generator function 506. Specifically, the trajectorymodification function 514 generates changes for the flight trajectory,or trajectory deltas, based on the weighted and limited avoidancecommands from the function 512. The trajectory modification function 514may then integrate the trajectory delta with a generated trajectory toproduce a new modified trajectory.

In specific embodiments, function 512 may output avoidance commands tochange heading rate, climb and descend rates, andacceleration/deceleration. The avoidance commands are then convertedinto delta trajectory commands based on the steering law for theaircraft, as well as the desired aircraft response to the steeringcommands. For example, the aircraft steering law may be configured toconvert heading change into a heading rate command based on aproportional control law with gain K. In such an instance, when anaircraft is predicted to breach a separate perimeter, a steeringadjustment algorithm of the trajectory modification function 514 mayproduce a heading delta, or change, by dividing a collision avoidanceheading rate command by K. In this case, the steering law will convertit back to a heading rate command. In another example, when thepre-determined trajectory generated by the trajectory generator function506 includes a set of way points, the trajectory modification function514 may include an adjustment algorithm that moves the next way point ofthe trajectory based on one or more avoidance commands. In this way, thedesired heading change may be produced to provide collision avoidance inthe event a separation perimeter is breached. Subsequent to thetrajectory modification, the new modified trajectory 524 may be passedon to the vehicle response function 504 to be implemented. The vehicleresponse function 504 may include the steering laws and vehicleresponse. In this way, these embodiments may provide collision avoidancewithout the need to modify aircraft control commands, (i.e., steeringlaw), as described in FIG. 3. Accordingly, collision avoidance may beimplemented as a separate function outside of the steering and flightcontrol functions, such as outside the trajectory generator function 502and the vehicle response function 504.

It will be appreciated that collision avoidance component 506 may beconfigured to continuously monitor the trajectories of the self-aircraftand the traffic aircraft and predict future “breaches” of the separationperimeter by the CPA avoidance computations between the aircraft. Inresponse, the trajectory modification function 514 may continuously makeadjustments to the flight trajectory whenever the “breaches” occur toensure that proper separation between aircraft is maintained.

FIG. 6 is a block diagram depicting a dynamic trajectory generator thatthat provides trajectory planning for a plurality of vehicles. Accordingto various embodiments, the dynamic trajectory generator 602 may be aground-based trajectory generator configured to provide “deconflicted”flight trajectories for a plurality of aircraft. In other words, theaircraft trajectories supplied by the dynamic trajectory generator 602are configured to maintain minimum separations between aircraft at alltimes. Specifically, deconflicted trajectories may be generated byrunning independently optimal but conflicted trajectories through asimulation that contains models of the vehicle dynamics, theirrespective separation control laws or mechanisms, and wind predictions.The processing of these trajectories by the dynamic trajectory generator602 provides the deconflicted trajectories.

As shown in FIG. 6, the dynamic trajectory generator 602 may beconfigured to receive data that includes traffic knowledge 604,separation limits 606, response limits 608, a look ahead time 610, windprediction 612, and aircraft models 614. In turn, the dynamic trajectorygenerator 602 may generate a plurality of aircraft flight trajectoriesbased on CPA computations. These trajectories may include 3-dimensionaltrajectories, and as well as 4-dimensional trajectories that dictate thepositions of the aircraft at a particular time.

The traffic knowledge 604 may include positions and flight trajectoriesof a plurality of traffic aircraft. According to various embodiments,the traffic sensing function 604 may be configured to receive trafficdata from a Traffic Alert and Collision Avoidance System (TCAS), anAutomatic Dependent Surveillance (ADS) system, a ground air trafficcontrol (ATC) system, or traffic surveillance sensor systems onboardaircraft, as well as other air traffic detection systems. In otherembodiments, traffic knowledge 604 may include flight trajectories fromflight plans, flight trajectories predicted trajectories from currentaircraft positions and velocities, and other predetermined flighttrajectories.

The separation limits 606 may be configured define the dimensions ofseparation perimeters between the plurality of aircraft. In oneimplementation, the separation limits 606 may define a minimumseparation distances between aircraft that extends in all directions. Insuch an implementation, the separation perimeter may be in the form asphere. For example, a separation perimeter may be established based onthe separation distance of one mile in all directions. In such as case,a plurality of aircraft are considered to have “breached” a separationperimeter if they are closer than one mile at their CPA. In otherimplementations, the separation limit function 606 may be configured toprovide other separation perimeter shapes, as well as multipleseparation layers, as described above.

The response limits 608 may determine the promptness at which theavoidance commands are carried out. For example, the response limits maybe established so that when the predicted CPA between the two trafficaircraft is likely to occur at a large range, the provision of the oneor more avoidance commands may be delayed. Conversely, if the predictedCPA between two aircraft is likely to occur at a small distance from anaircraft's position, the aircraft may be provided one or more immediateavoidance commands. It will be appreciated that the response limits maybe set to increase the likelihood of separation using minor correctionsat long range, or to meet other optimization objectives. In otherembodiments, the response limit may include time limitations for theexecution of avoidance commands. For example, if the CPA is likely tooccur far in the future, such as beyond a predetermined time interval,an avoidance command may be delayed. Conversely, if the CPA is imminentin time, such as before a predetermined time interval expires, avoidancecommands may be rapidly provided. The implementation of time limitationsas response limits may also be suitable for collision avoidance betweenaircraft with long TCPA duration such as those that are flying information at close range along parallel paths, and in trail, or head ontrajectories at far range with near zero closest point of approachdistance.

The look ahead time 610 includes specific time horizons for which thedynamic trajectory generator 602 is to generate the flight trajectoriesfor a plurality of aircraft. The wind predictions 612 include wind datawhich may be used by the dynamic trajectory generator 602 to plot theflight trajectories. In some embodiments, the wind prediction 612 may beobtained from aviation weather reports such as METAR reports, TerminalAerodrome Forecasts (TAF) from the National Weather Service (NWS), aswell as other meteorological report sources. The aircraft models 614 mayinclude aircraft performance data. Such performance data may includeaircraft steering laws, aircraft control laws, performance dynamics andcapabilities.

The dynamic trajectory generator 602 may be configured to runsimulations using the data inputs 604-614 to generate deconflictedflight trajectories for a plurality of aircraft. For instance, theflight trajectories derived from traffic knowledge 604 may be used bythe dynamic trajectory generator 602 to predict whether at their closestpoint of approach (CPA), a plurality of aircraft are expected to“breach” a predetermined separation perimeter as determined by theseparation limits 606. Based on these predictions, the dynamictrajectory generator 602 may change the flight trajectories to generatedeconflicted trajectories that eliminate these separation perimeterbreaches. In various implementations, the simulations may be conductedusing the exemplary equations shown in FIG. 4. Moreover, the dynamictrajectory generator 602 may be configured use to the response limits608 to tailor the trajectory changes, similar to those described in FIG.5 b. In some implementations, the dynamic trajectory generator 602 mayalso account for wind predictions 612. For example, trajectory changesmay be modified using the wind predictions 612 so that any of theirinfluence on flight trajectories may be countered and nullified. Infurther embodiments, the dynamic trajectory generator 602 may also takeinto consideration the aircraft models 614 to design flight trajectoriesthat conform to the performance capabilities of the aircraft.

Once the deconflicted trajectories have been determined for a pluralityof aircraft, the dynamic trajectory generator 602 may use the aircraftmodels 614 to translate the deconflicted trajectories into controlcommands for implementation with each of the plurality of aircraft. Thecontrol commands may include heading rate change commands, climb ordescend rate modification commands, acceleration and decelerationcommands, and other steering commands such as speed, altitude, andheading alteration commands. Alternatively, the dynamic trajectorygenerator 602 may provide the flight trajectories to the aircraft forimplementation by an autopilot or flight management system onboard theeach aircraft, such as aircraft 616-622. It will be appreciated that thesimulations may be continually executed by the dynamic trajectorygenerator 602 out to a specified time horizon using current aircraftstate information and proposed trajectories or intentions.

FIG. 7 is a side elevational view of an aircraft 700 in accordance withan embodiment of the present disclosure. In general, except for one ormore systems in accordance with the present disclosure, the variouscomponents and subsystems of the aircraft 700 may be of knownconstruction and, for the sake of brevity, will not be described indetail herein. As shown in FIG. 7, the aircraft 700 includes one or morepropulsion units 704 coupled to a fuselage 702, a cockpit 706 in thefuselage 702, wing assemblies 708 (or other lifting surfaces), a tailassembly 710, a landing assembly 712, a control system (not visible),and a host of other systems and subsystems that enable proper operationof the aircraft 700. At least one component of a vehicle-centriccollision avoidance system 714 formed in accordance with the presentdisclosure is located within the fuselage 702. However, components ofthe collision avoidance system 714 may be distributed throughout thevarious portions of the aircraft 700.

Although the aircraft 700 shown in FIG. 7 is generally representative ofa commercial passenger aircraft, including, for example, the 737, 747,757, 767, 777, and 787 models commercially-available from The BoeingCompany of Chicago, Ill., the inventive apparatus and methods disclosedherein may also be employed in the assembly of virtually any other typesof aircraft. More specifically, the teachings of the present disclosuremay be applied to the manufacture and assembly of other passengeraircraft, cargo aircraft, rotary aircraft, and any other types ofaircraft, including those described, for example, in The IllustratedEncyclopedia of Military Aircraft by Enzo Angelucci, published by BookSales Publishers, September 2001, and in Jane's All the World's Aircraftpublished by Jane's Information Group of Coulsdon, Surrey, UnitedKingdom. It may also be appreciated that alternate embodiments of systemand methods in accordance with the present disclosure may be utilized inother aerial vehicles, both manned and unmanned, as well as otherhardware such as, satellites, robots, etc.

It should be appreciated that the illustrated avionics system 200 isonly one example of a suitable operating environment and is not intendedto suggest any limitation as to the scope of use or functionality of theinvention. Other avionic environments and/or configurations may besuitable for use with the invention. For example, the exemplarycollision avoidance computer 212 may a part of an autopilot 206. Inother exemplary instances, one or more of the modules 218-228, as wellas database 230, may be directly implemented on the autopilot 206,flight director 208, or any other suitable avionic component, navigationsystem, or any avionic system present in an aircraft that is capable ofreceiving, processing, and storing data.

Embodiments of systems and methods in accordance with the presentdisclosure may provide significant advantages over the prior art. Thevehicle-centric collision avoidance systems in accordance with thevarious embodiments may advantageously alter the flight paths of one ormore aircraft based when their predicted closest point of approach (CPA)is expected to breach a predefined separation perimeter. In this way,collision avoidance may be performed without human intervention.Automated collision avoidance may reduce or eliminate the possibility ofhuman error or improperly performed collision avoidance maneuvers.Moreover, the vehicle-centric collision avoidance systems in accordancewith the various embodiments may diminish the need for ground airtraffic controllers to direct aircraft separation. Such labor savingsmay make it possible for the air traffic controller to manage a largernumber of aircraft than previously possible. Lastly, the vehicle-centriccollision avoidance system may also be implemented on unmanned aircraftto enable better control and performance.

While various embodiments have been illustrated and described above,many changes can be made without departing from the spirit and scope ofthe embodiments. Accordingly, the scope of the embodiments is notlimited by the disclosure of these embodiments. Instead, the scopeshould be determined entirely by reference to the claims that follow.

What is claimed is:
 1. A computer readable storage device comprising computer-readable instructions which, when executed by a processor, cause the processor to at least: determine a first flight trajectory for a first aircraft; determine a second flight trajectory for a second aircraft; predict a distance between the first aircraft and the second aircraft at a predicted closest point of approach based on the first and second flight trajectories; compare the distance to a separation perimeter layer, the separation perimeter layer configured to provide at least a threshold separation distance from the first aircraft to the second aircraft; and in response to the distance breaching the separation perimeter layer and without human input, alter the first flight trajectory.
 2. The storage device as defined in claim 1, wherein the instructions are further to cause the processor to compute a first direction from a current position of the first aircraft to the predicted closest point of approach, the instructions to cause the processor to alter the first flight trajectory by altering the first flight trajectory in a second direction that is different than the first direction.
 3. The storage device as defined in claim 1, wherein the instructions are to cause the processor to predict the distance by continuously predicting the distance to the separation perimeter layer as the first aircraft moves along the first flight trajectory, the instructions to further cause the processor to reinstate at least a portion of the first flight trajectory when the distance does not breach the separation perimeter layer.
 4. The storage device as defined in claim 1, wherein the instructions are further to cause the processor to reinstate at least a portion of the first flight trajectory when the distance between the first aircraft and the second aircraft at the predicted closest point of approach does not breach the separation perimeter layer.
 5. The storage device as defined in claim 1, wherein the instructions are further to cause the processor to generate flight control commands to cause the first aircraft to implement the first flight trajectory, the instructions to cause the processor to alter the first flight trajectory by assigning a gain prior to implementing the first flight trajectory as flight control commands.
 6. The storage device as defined in claim 1, wherein the instructions are further to cause the processor to predict a time to reach the predicted closest point of approach from a current position of the first aircraft, the instructions to cause the processor to alter the first flight trajectory by altering the first flight trajectory using a magnitude that varies inversely to a duration of the time to reach the predicted closest point of approach.
 7. The storage device as defined in claim 1, wherein the instructions are to cause the processor to alter the first flight trajectory by altering the first flight trajectory using a magnitude that varies inversely to a length of the predicted distance between the first aircraft and the second aircraft at the predicted closest point of approach.
 8. An aircraft, comprising: a structural assembly; a trajectory generator to determine a first flight trajectory for the aircraft; and a collision avoidance component to: predict a distance between the aircraft and a second aircraft at a predicted closest point of approach based on the first flight trajectory and a second flight trajectory; compare the distance to a separation perimeter layer, the separation perimeter layer configured to provide at least a threshold separation distance from the aircraft to the second aircraft; and in response to the distance breaching the separation perimeter layer and without human input, alter the first flight trajectory.
 9. The aircraft as defined in claim 8, wherein the collision avoidance component is to compute a first direction from a current position of the aircraft to the predicted closest point of approach, the collision avoidance component to alter the first flight trajectory by altering the first flight trajectory in a second direction that is different than the first direction.
 10. The aircraft as defined in claim 8, wherein the collision avoidance component is to predict the distance by continuously predicting the distance to the separation perimeter layer as the aircraft moves along the first flight trajectory, the collision avoidance component to reinstate at least a portion of the first flight trajectory when the distance does not breach the separation perimeter layer.
 11. The aircraft as defined in claim 8, wherein the collision avoidance component is to reinstate at least a portion of the first flight trajectory when the distance between the aircraft and the second aircraft at the predicted closest point of approach does not breach the separation perimeter layer.
 12. The aircraft as defined in claim 8, wherein the collision avoidance component is to generate flight control commands to cause the aircraft to implement the first flight trajectory, the collision avoidance component to alter the first flight trajectory by assigning a gain prior to implementing the first flight trajectory as flight control commands.
 13. The aircraft as defined in claim 8, wherein the collision avoidance component is to predict a time to reach the predicted closest point of approach from a current position of the aircraft, the collision avoidance component to alter the first flight trajectory by altering the first flight trajectory using a magnitude that varies inversely to a duration of the time to reach the predicted closest point of approach.
 14. The aircraft as defined in claim 8, wherein the collision avoidance component is to alter the first flight trajectory by altering the first flight trajectory using a magnitude that varies inversely to a length of the predicted distance between the aircraft and the second aircraft at the predicted closest point of approach.
 15. The aircraft as defined in claim 8, wherein the trajectory generator is to determine the second flight trajectory for the second aircraft.
 16. The aircraft as defined in claim 8, wherein the aircraft comprises an unmanned aircraft.
 17. A method comprising: determining a first trajectory for a first vehicle; determining a second trajectory for a second vehicle; predicting a distance between the first vehicle and the second vehicle at a predicted closest point of approach based on the first and second trajectories; comparing the distance to a separation perimeter layer, the separation perimeter layer configured to provide at least a threshold separation distance from the first vehicle to the second vehicle; and in response to the distance approaching the separation perimeter layer and without human input, altering the first trajectory to avoid a breach of the separation perimeter layer by the first vehicle or second vehicle.
 18. The method as defined in claim 17, further comprising altering the second trajectory of the second vehicle automatically and without human input in response to the distance approaching the separation perimeter layer.
 19. The method as defined in claim 18, wherein altering the second trajectory decreases an amount of alteration of the first trajectory to avoid a breach of the separation perimeter layer.
 20. The method as defined in claim 19, wherein the second vehicle resumes the second trajectory after determining that the distance between the first vehicle and the second vehicle at the predicted closest point of approach is not approaching the separation perimeter layer. 